1. Field of the Invention
The present invention relates to a solid-state image sensor, and more particularly, it relates to a solid-state image sensor comprising a shielding material line for blocking light incident from above a prescribed pixel upon another pixel adjacent to the prescribed pixel.
2. Description of the Background Art
Various solid-state image sensors each comprising a shielding material line for blocking light incident from above a prescribed pixel upon another pixel adjacent to the prescribed pixel are known in general. Such a solid-state image sensor is disclosed in ITE Technical Report Vol. 28, No. 25, pp. 13-16, IST2004-25 (May, 2004), for example.
FIG. 16 is a plan view showing the structure of an imaging portion of an exemplary conventional solid-state image sensor comprising shielding material lines. FIG. 17 is a sectional view of the imaging portion of the exemplary conventional solid-state image sensor taken along the line 700-700 in FIG. 16. FIG. 18 is a sectional view of the imaging portion of the exemplary conventional solid-state image sensor taken along the line 750-750 in FIG. 16. Referring to FIG. 16, the imaging portion of the exemplary conventional solid-state image sensor comprising shielding material lines is provided with a plurality of pixels 101. Photoelectric conversion portions 102 are provided on regions corresponding to the pixels 101 respectively.
A plurality of transfer gates 103 for transferring electrons generated by the photoelectric conversion portions 102 are provided to extend along a direction perpendicular to an electron transfer direction (along arrow A) at prescribed intervals. Three such transfer gates 103 are provided every pixel 101. Among the three transfer gates 103 provided in correspondence to each pixel 101, the central transfer gate 103a enters an ON-state in photoreception. Thus, a potential well is formed on a region located under the central transfer gate 103a of the three transfer gates 103 in photoreception, for storing electrons generated by photoelectric conversion in this potential well. Shielding material lines 104 are provided on regions located between adjacent pairs of pixels 101 arranged along the direction perpendicular to the electron transfer direction (along arrow A) above the transfer gates 103 to extend along the electron transfer direction (along arrow A). Each shielding material line 104 is provided for suppressing incidence of light from above a prescribed pixel 101 upon another pixel 101 adjacent to the prescribed pixel 101 in the direction perpendicular to the electron transfer direction (along arrow A).
In the imaging portion of the exemplary conventional solid-state image sensor, a plurality of gate insulating films 106 are formed on the upper surface of a substrate 105 at prescribed intervals, as shown in FIG. 17. The substrate 105 is formed with the photoelectric conversion portions 102 corresponding to the aforementioned pixels 101 respectively, as shown in FIG. 18. The aforementioned transfer gates 103 are formed on the gate insulating films 106 respectively. An insulating film 107 is formed to cover the gate insulating films 106 and the transfer gates 103. The aforementioned shielding material lines 104 are formed on prescribed regions of the insulating film 107. The shielding material lines 104 and the transfer gates 103 are at a prescribed distance d.
In the exemplary conventional solid-state image sensor comprising the shielding material lines 104 shown in FIG. 16, however, unintentional incident light may be obliquely incident from above a prescribed pixel 101 upon another pixel 101 adjacent to the prescribed pixel 101 through a region located under the corresponding shielding material line 104, as shown in FIG. 18. In this case, color mixture disadvantageously results from the incidence of the unintentional incident light upon the pixel 101 adjacent to the prescribed pixel 101. This problem of color mixture may conceivably be solved by approaching the shielding material lines 104 toward the substrate 105 thereby blocking the aforementioned unintentional oblique incident light with the corresponding shielding material line 104. In this case, however, the interval between the corresponding shielding material line 104 and all transfer gates 103 intersecting with the shielding material line 104 through the insulating film 107 is disadvantageously reduced. Thus, capacitances between the shielding material line 104 and the corresponding transfer gates 103 are disadvantageously increased to increase load capacitances of the transfer gates 103 or easily cause a short circuit between two adjacent transfer gates 103 through the shielding material line 104.